The present invention relates to an X-ray imaging device that captures an image in a decubitus posture, an upright posture, mammography, or the like and a calibration method therefor, and more particularly, to an X-ray imaging device that can correct a misalignment even when a movement axis of an X-ray source has the misalignment with respect to an X-ray detector, that can obtain a high-precision synthesis image (tomosynthesis image) of a cross section at a predetermined position of a subject, and that furthermore can suppress aging degradation of the misalignment and a calibration method therefor.
Recently, in order to observe an affected part in detail, various X-ray imaging devices that can perform a tomosynthesis imaging operation, in which an image with a desired tomographic plane emphasized can be obtained by irradiating a subject with X-rays from different angles while moving an X-ray source, capturing images, and adding the captured images have been proposed (for example, see JP 2011-67503 A).
In the tomosynthesis imaging, for example, an X-ray source is moved to be parallel to an X-ray detector or to draw an arc of a circle, an ellipse, or the like, plural captured images are obtained by imaging a subject at different irradiation angles, and the captured images are reconstructed to create a tomographic image.
JP 2011-67503 A discloses a radiographic imaging device in which any one of a first mode in which only a radiation source is moved and a second mode in which both the radiation source and detection means are moved can be selected depending on imaging conditions at the time of tomosynthesis imaging and plural captured images are acquired in the selected mode.
However, in the tomosynthesis imaging, precise alignment of a movement axis of the X-ray source with respect to the X-ray detector (X-ray image sensor) is required. Particularly, in an X-ray imaging device using an overhead traveling X-ray source, the X-ray source and the X-ray detector (X-ray image sensor) are not integrated as a unified body and it is thus not easy to install the X-ray source and the X-ray detector with high-precision alignment.
In the conventional tomosynthesis imaging, a method of creating calibration data using a predetermined marker assembly is known. However, this method has difficulties in that it is necessary to manage preciseness of markers, it is necessary to create calibration data for each imaging condition such as an SID (distance between a focal point of an X-ray tube and an image-receiving plane), an angle of an X-ray source, and the number of shots, and the like.
Moreover, in the method of creating calibration data using a predetermined marker assembly, since previously-acquired calibration data is used, there is a problem in that it is not possible to cope with aging degradation (aging variation).
Other than that described above, a method of detecting positional misalignment of an image using a marker and correcting an X-ray image is known (for example, see JP 2000-278606 A).
JP 2000-278606 A discloses an X-ray imaging device in which a supporter having a marker is attached to an imaging region of a subject, a mask image and a live image of the imaging region are captured, an error between the position of the marker in the mask image and the position of the marker in the live image is calculated and subtraction is carried out so as to match both positions with each other, and thereby occurrence of noise in the subtraction image generated due to positional misalignment in a catheterization table is prevented.
Even in this case, there is a problem in that it is necessary to manage preciseness of the marker in order to create calibration data, it is necessary to create calibration data for each imaging condition such as an SID (distance between a focal point of an X-ray tube and an image-receiving plane), an angle of an X-ray source, and the number of shots, and the like.
JP 2010-252951 A discloses X-ray CT equipment that is suitable for use in clinical site and that is intended to acquire a highly precise CT image without a ring artifact. In the X-ray CT equipment disclosed in JP 2010-252951 A, when a ring artifact is detected from an output image, an air calibration data acquiring unit acquires new air calibration data and an air calibration data replacing unit replaces the air calibration data used up to that time point with the new air calibration data.
As described above, JP 2010-252951 A discloses that the air calibration data is replaced, but JP 2010-252951 A relates to X-ray CT equipment. Under the circumstances, an X-ray imaging device that can cope with aging degradation of calibration in tomosynthesis imaging is not known.